It's fairly easy to head to Google Voice's homepage, paste in a number, type out a contact, then click a button to call. It's far easier, however, to use Ubiquity with Firefox to highlight a number and just type "call."

The earth2marsh site posts a Ubiquity command that requires just a little bit of configuration to hook up with your Google Voice account. Once it's set up, however, making a call with your pre-determined default phone is a simple matter of highlighting a number, activating Ubiquity, and using the action verb "call." Need help using or adding commands into Ubiquity? Check out Gina's guide to making Ubiquity your ultimate Firefox commander.